Try a couple of old drawers at first — trunks hold me in (9)
I believe the answer is:
'trunks hold me in' is the definition.
(heartwood is part of a tree trunk)
'try a couple of old drawers at first' is the wordplay.
'try' becomes 'hear' (as in to try someone in court or hear their case).
'a couple of' becomes 'two'.
'at first' indicates taking the first letters.
The first letters of 'old drawers' is 'od'.
(Another definition for heartwood that I've seen is " hard stuff".)